The Aral Basin: Evolution and oil and gas presence

Category Tectonic & Seismotectonic
Group GSI.IR
Location International Geological Congress,oslo 2008
Author Uzhkenov, Bulat۱; Davydov, Nikolay۲; Davydov, Arthur۳
Holding Date 27 September 2008

The Aral sedimentary Basin (AB) was formed in the limits of junction zone of Usturt and Kyzylkum microcontinents, isolating in Late Paleozoic – Early Mesozoic Periods as Aral-Torgay link of East Ural riftogenious system with linearly-extended depressions filled up by terrigene Permian-Triassic and Jurassic sediments. Nowadays the AB is one of the most oil-and-gas perspectives in Kazakhstan after the Caspian. The results of 25-years geology-geophysical and drilling researches were summed up and they are based on the data of newest high-resolution MOGT-2D seismic works and new wells’ drilling (Tunguruksor D1; Kushokinsk P2; Tobebulak P1; Kylandy W - 1, 2 and East 1 and others). The Aral area includes: Aral Sea, Kosbulak, Sudochiy and East Aral depressions. The basic evolution stages of AB were considered. Brand new methods of estimation of AB’s oil-and-gas perspectives in a view of studying a quasi-platform intermediate structure level were suggested and offered in accordance with new data of Kazakhstan and Uzbekistan researches. Within the limits of the AB more than 25 positive local structures were discovered, oil-and-gas evidences were shown in the Carboniferous, Jurassic, Cretaceous and Paleogene Periods’ sediments. The results of seismic works had allowed considerably enlarging the thickness in 1000 m of Upper Triassic - Down Jurassic complexes of sediments and increasing its oil-and-gas perspectives. Uninvestigated traps of non-structural type within the limits of the AB have a high oil-and-gas potential. On area of the AB’s Southern part were discovered 11 gas/gas-condensate fields in Upper- Middle Jurassic terrigene sediments. An AB’s Pre-Jurassic complex of rocks is worth special interest, where deposits of Upper Carboniferous-Low Permian and Upper Devonian-Low Carboniferous are attributed to the oil-and-gas producing sediments in Pre-Jurassic complex. An oil-and-gas inflows were received out of Paleozoic sediments (gas deposits Kokchalak, Chibiny from carbonaceous sediments (depths 3,5-3,7 km, production rate up to 500 thnd m3/day); an oil from Karakuduk).
The estimation of oil-and-gas content of quasi platform complex of the AB with thickness 2-6 km was conducted. It is proved that in the shore of Aral Sea there is carbonate-terrigene thickness of Upper Devonian-Middle Carboniferous under the powerful thickness of Permian molassa sediments’ thickness, where in the Southern part of the AB a group of gas/gas condensate fields is located. As results of works the zones with concentration of potential reserves of hydrocarbons (in thnd tons on 1 sq.km) were allocated on prognoses "Map of oil-and-gas content’s prospects of the AB" and a modern division into districts by oil-and-gas bearing degree of the AB was executed. New geological factors are dictating a necessity of correctives in the program of oil-and-gas content’ s of the AB and building a new geological model. Was discovered a new oil-and-gas province in Kazakhstan - Aral Basin